There has been known, as an information recording medium (hereinafter referred to as a “recording medium” or a “medium”) that is capable of recording and reproducing information at high speed, and has a large capacity, an optical information recording medium typified by Digital Versatile/Video Disc (DVD) and Blu-ray Disc. This optical information recording medium performs recording and reproduction of information by making use of variation in reflectance in two different states and has such a large advantage that can optionally perform a random access and is also excellent in portability. Therefore, importance thereof has recently increased more and more.
Examples of a conventional optical information recording medium include a rewritable medium capable of rewriting many times, a write-once medium capable of writing only one time, and a reproduction-only medium capable of only reproducing. In general, the reproduction-only medium is easy to be manufactured and can be provided at low costs since the number of layers constituting the medium can be reduced as compared with the rewritable medium and write-once medium. Therefore, the reproduction-only medium has widely been used as a medium that distributes digital contents such as music, movie and game software.
Patent Document 1 discloses that, in a reproduction-only medium, sub-information such as a serial number of a medium is recorded by a barcode-shaped mark called as Burst Cutting Area (BCA), in addition to main information such as image and voice, and then processed by burning off an information recording layer (reflective film) using a YAG laser.
Also, Patent Document 2 discloses formation of a recording layer made of an alloy containing, as main components, at least one kind of an element selected from the group consisting of [Ge, Si, Sn] elements and at least one kind of an element selected from the group consisting of [Au, Ag, Al, Cu] elements, as a recording material of a write-once medium.
Furthermore, Patent Document 3 discloses an optical recording medium including an information layer equipped with a reflective film formed with an information recording part by a physical shape change, wherein the reflective film is capable of performing additional recording by thermography and is made of an Al alloy or Cu alloy having electrical resistivity of 20 μΩ·cm or more and 90 μΩ·cm or less. The same document discloses that this reflective film is preferably made of the Al alloy or Cu alloy containing one or more kinds of elements selected from at least Ti, Si, Cu, Al, Fe, W, Cr, O, Ar, Mg and Tb added therein. It becomes possible for the user to record the position where reproduction was finished and a mark of a game over point in game software in a reproduction-only optical recording medium by providing such a reflective film. Entry of the algorithm capable of decrypting data achieved by entry of encryption data makes it impossible to reproduce an illegally copied optical recording medium.